Method and apparatus for electrochemical planarization of a workpiece

ABSTRACT

An electrochemical planarization apparatus for planarizing a metallized surface on a workpiece includes a polishing pad and a platen. The platen is formed of conductive material, is disposed proximate to the polishing pad and is configured to have a negative charge during at least a portion of a planarization process. At least one electrical conductor is positioned within the platen. The electrical conductor has a first end connected to a power source. A workpiece carrier is configured to carry a workpiece and press the workpiece against the polishing pad. The power source applies a positive charge to the workpiece via the electrical conductor so that an electric potential difference between the metallized surface of the workpiece and the platen is created to remove at least a portion of the metallized surface from the workpiece.

TECHNICAL FIELD

[0001] The present invention relates, generally, to systems forpolishing or planarizing workpieces, such as semiconductor wafers. Moreparticularly, it relates to an apparatus and method for electrochemicalplanarization of a wafer having a metallized surface.

BACKGROUND

[0002] The production of integrated circuits begins with the creation ofhigh-quality semiconductor wafers. During the wafer fabrication process,the wafers may undergo multiple masking, etching, and dielectric andconductor deposition processes. In addition, metallization, whichgenerally refers to the materials, methods and processes of wiringtogether or interconnecting the component parts of an integrated circuitlocated on the surface of a wafer, is critical to the operation of asemiconductor device. Typically, the “wiring” of an integrated circuitinvolves etching trenches and “vias” in a planar dielectric (insulator)layer and filling the trenches and vias with a metal.

[0003] In the past, aluminum was used extensively as a metallizationmaterial in semiconductor fabrication due to the leakage and adhesionproblems experienced with the use of gold, as well as the high contactresistance which copper experienced with silicon. Other metallizationmaterials have included Ni, Ta, Ti, W, Ag, Cu/Al, TaN, TiN, CoWP, NiPand CoP. Over time, the semiconductor industry has slowly been moving tothe use of copper for metallization due to the alloying andelectromigration problems that are seen with aluminum. When copper isused as the trench and via filling material, typically a barrier layerof another material is first deposited to line the trenches and vias toprevent the migration of copper into the dielectric layer. Barriermetals may be W, Ti, TiN, Ta, TaN, various alloys, and other refractorynitrides, which may be deposited by CVD, PFD, or electrolytic plating.To achieve high quality filling of the trenches and vias, extra metal isoften deposited over areas of the wafer above and outside the trenchesand vias. After filling, planarization is typically conducted to removethe extra metal down to the dielectric surface. Planarization leaves thetrenches and vias filled and results in a flat, polished surface.

[0004] Because of the high degree of precision required in theproduction of integrated circuits, an extremely flat surface isgenerally needed on at least one side of the semiconductor wafer tooptimize the fabrication process, as well as to ensure proper accuracyand performance of the microelectronic structures created on the wafersurface. As the size of the integrated circuits continues to decreaseand the density of microstructures on an integrated circuit increases,the need for precise wafer surfaces becomes more important. Therefore,between each processing step, it is usually necessary to polish orplanarize the surface of the wafer to obtain the flattest surfacepossible.

[0005] Chemical mechanical planarization (CMP) is a techniqueconventionally used for planarization of semiconductor wafers. For adiscussion of chemical mechanical planarization (CMP) processes andapparatus, see, for example, Arai et al., U.S. Pat. No. 4,805,348,issued February 1989; Arai et al., U.S. Pat. No. 5,099,614, issued March1992; Karlsrud et al., U.S. Pat. No. 5,329,732, issued July 1994;Karlsrud, U.S. Pat. No. 5,498,196, issued March 1996; and Karlsrud etal., U.S. Pat. No. 5,498,199, issued March 1996.

[0006] Typically, a CMP machine includes a wafer carrier configured tohold, rotate, and transport a wafer during the process of polishing orplanarizing the wafer. During a planarization operation, a pressureapplying element (e.g., a rigid plate, a bladder assembly, or the like)that may be integral to the wafer carrier, applies pressure such thatthe wafer engages a polishing surface with a desired amount of force.The carrier and the polishing surface are rotated, typically atdifferent rotational velocities, to cause relative lateral motionbetween the polishing surface and the wafer and to promote uniformplanarization.

[0007] In general, the polishing surface comprises a horizontalpolishing pad that has an exposed abrasive surface of, for example,cerium oxide, aluminum oxide, fumed/precipitated silica or otherparticulate abrasives. Polishing pads can be formed of variousmaterials, as is known in the art, and are available commercially.Typically, the polishing pad may be blown polyurethane, such as the ICand GS series of polishing pads available from Rodel ProductsCorporation in Scottsdale, Ariz. The hardness and density of thepolishing pad depend on the material that is to be polished. An abrasiveslurry may also be applied to the polishing surface. The abrasive slurryacts to chemically weaken the molecular bonds at the wafer surface sothat the mechanical action of the polishing pad can remove the undesiredmaterial from the wafer surface.

[0008] While CMP tends to work very well for planarization if thecorrect slurry and process parameters are used, it may leave stresses inthe worked workpiece, leading to subsequent cracking and shortingbetween metal layers. In addition, the semiconductor industry isincreasingly using low k dielectrics, which tend to be fragilematerials. CMP may result in shearing or crushing of these fragilelayers. CMP also has a tendency to cause dishing in the center of widemetal features, such as trenches and vias, oxide erosion between metalfeatures, and oxide loss of the dielectric.

[0009] Electrochemical planarization is an attractive alternative to CMPbecause it does not impart significant mechanical stresses to theworkpiece and, consequently, does not significantly reduce the integrityof the low k dielectric devices. Further, electrochemical planarizationis less likely to cause dishing, oxide erosion and oxide loss of thedielectric layer.

[0010] Electrochemical planarization is based on electroetching andelectrochemical machining, that is, the removal of a thin layer of metalfrom a substrate by the combination of an electrochemical solution andelectricity. FIG. 1 shows a conventional prior art electroetching cell.A tank 2 holds a liquid electrolyte 4, such as an aqueous solution of asalt. Two electrodes, an anode 6 and a cathode 8, are wired to a currentsource, such as a battery 10. When the apparatus is electrified, metalatoms in the anode 6 are ionized by the electricity and go into thesolution as ions. Depending on the chemistry of the metals and salt, themetal ions from anode 6 either plate the cathode 8, fall out asprecipitate, or remain in solution.

[0011] When used for planarization of metal films on semiconductorwafers, conventional electrochemical planarization presents thedisadvantage that the metal may not be selectively removed from thewafer. While existing electrochemical planarization techniques are knownto “smooth” a metal layer, they are limited by topography dimensions anddo not achieve true planarization. FIG. 2 shows a dielectric layer 12having trenches, or vias, and having a barrier metal layer 20 thereon. Ametal layer 14 is deposited on the wafer over the barrier layer, fillingthe trenches. After being deposited on barrier layer 20, metal layer 14may not be completely flat but, rather, may have areas of hightopography 16 and low topography 18. With conventional electrochemicalplanarization, when the areas of high topography and low topography areof large dimension, selectivity of etching is reduced and the metallayer is removed uniformly, so that the areas of high topography and lowtopography remain. In addition, chemical saturation may act to inhibitselective etching in areas of small dimension topography. At the startof a conventional electrochemical planarization process, metal ionsdissociate from the metal layer and enter the electrolytic solution,saturating the electrolytic solution close to the metal layer. Whencurrent is applied, a rapid increase of metal ions into the solutioncreates an “anode film.” As the anode film becomes saturated with metalions, the planarization process slows down or stops in response to theincrease in the anode film metal ion saturation level. Thus, withconventional electrochemical planarization, uniform planarization is notachieved.

[0012] For uniform planarization, “step-height reduction” is desired,that is, the selective removal of the metal layer at the high topographyareas, followed by uniform removal of the metal layer, both locally andglobally. Step-height reduction should result in metal remaining only inthe trenches and vias with a flat surface therein, as illustrated inFIG. 3.

[0013] Accordingly, there exists a need for an electrochemicalplanarization method and apparatus which accomplishes improvedstep-height reduction of metal layers on substrates, followed by uniformplanarization of the metal layer.

SUMMARY OF THE INVENTION

[0014] These and other aspects of the present invention will become moreapparent to those skilled in the art from the following non-limitingdetailed description of preferred embodiments of the invention takenwith reference to the accompanying figures.

[0015] In accordance with an exemplary embodiment of the presentinvention, an electrochemical planarization apparatus for planarizing ametallized surface on a workpiece includes a polishing pad and a platen.The platen is formed of conductive material, is disposed proximate tothe polishing pad, and is configured to have a negative charge during atleast a portion of a planarization process. A workpiece carrier isconfigured to carry a workpiece and press the workpiece against thepolishing pad. At least one electrical conductor is positioned withinthe platen and has a first end connected to a power source. The powersource applies a positive charge to the workpiece via the electricalconductor so that an electric potential difference between themetallized surface of the workpiece and the platen is created to removeat least a portion of the metallized surface from the workpiece.

[0016] In accordance with another embodiment of the present invention,the electrochemical planarization apparatus includes a solutionapplication mechanism configured to supply a first electrolyticplanarizing solution to a polishing surface of the polishing pad.

[0017] In accordance with a further embodiment of the present invention,the electrolytic planarizing solution includes a film forming agent forfacilitating the formation of a passivation layer on the metallizedsurface of the workpiece.

[0018] In accordance with yet another embodiment of the presentinvention, the electrochemical planarization apparatus includes at leasta first group and a second group of electrical conductors. A firstcurrent is supplied to the first group and a second current is suppliedto the second group.

[0019] In accordance with yet a further embodiment of the presentinvention, the electrochemical planarization apparatus includes anendpoint detection apparatus configured to detect an endpoint of aplanarization process of a workpiece.

[0020] In accordance with another exemplary embodiment of the presentinvention, a method of planarizing a metallized surface on a workpieceincludes: providing a polishing pad; providing a platen formed of aconductive material and disposed proximate to the polishing pad;providing a plurality of electrical conductors positioned within theplaten; pressing the workpiece against the polishing pad while causingrelative motion between the workpiece and the electrical conductors; andestablishing an electric potential difference between the metallizedsurface of the workpiece and the platen.

BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Exemplary embodiments of the present invention will hereafter bedescribed in conjunction with the appended drawing figures, wherein likedesignations denote like elements, and:

[0022]FIG. 1 is a schematic illustration of an electroetching cell ofthe prior art;

[0023]FIG. 2 is a cross-sectional view of a substrate with a metallayer;

[0024]FIG. 3 is a cross-sectional view of a substrate with metal-filledtrenches;

[0025]FIG. 4 is a cross-sectional view of a polishing pad and platen inaccordance with an exemplary embodiment of the present invention;

[0026]FIG. 5 is a top view of a polishing pad and platen in accordancewith an embodiment of the present invention;

[0027]FIG. 6 is a cross-sectional view of a wafer with a metallizedsurface contacting a polishing pad and contact element in accordancewith an exemplary embodiment of the present invention;

[0028]FIG. 7 is a cross-sectional view of a wafer after electrochemicalplanarization;

[0029]FIG. 8 is a top view of a platen in accordance with an embodimentof the present invention;

[0030]FIG. 9 is a top view of a polishing pad and platen in accordancewith another exemplary embodiment of the present invention;

[0031]FIG. 10 is an exploded perspective view of a platen in accordancewith another exemplary embodiment of the present invention; and

[0032]FIG. 11 is a cross-sectional view of another exemplary embodimentof the electrochemical planarization apparatus of the present invention.

[0033] Skilled artisans will appreciate that elements in the figures areillustrated for simplicity and clarity and have not necessarily beendrawn to scale. For example, the dimensions of some of the elements inthe figures may be exaggerated relative to other elements to help toimprove understanding of embodiments of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

[0034] The following description is of exemplary embodiments only and isnot intended to limit the scope, applicability or configuration of theinvention in any way. Rather, the following description provides aconvenient illustration for implementing exemplary embodiments of theinvention. Various changes to the described embodiments may be made inthe function and arrangement of the elements described without departingfrom the scope of the invention as set forth in the appended claims.

[0035] A schematic representation of an exemplary embodiment of anelectrochemical planarization (ECP) apparatus 30 of the presentinvention is illustrated in FIG. 4. The ECP apparatus 30 may usechemical mechanical planarization (CMP) in addition to electrochemicaletching to planarize the metallized surfaces of workpieces. To effectelectrochemical etching, ECP apparatus 30 utilizes an insulativepolishing pad 40 supported by a platen 50. A wafer 60 with a metallizedsurface 80 may be urged against polishing pad 40 by a wafer carrierassembly 130. Polishing pad 40 may be of the same diameter of wafer 60or may have a larger or smaller diameter than wafer 60. Platen 50 may befabricated from a conductive material, such as copper, tantalum, gold orplatinum or may be formed of an inexpensive material, such as aluminumor titanium, coated with a conductive material such as platinum, gold ortitanium. Platen 50 is connected to a power source 90 which isconfigured to establish an electric potential difference between platen50 and metallized surface 80, as described in more detail below. Platen50 may be connected to a driver or motor assembly (not shown) that isoperative to rotate platen 50 and polishing pad 40 about a verticalaxis. It will be appreciated, however, that the driver or motor assemblymay be operative to move platen 50 and polishing pad 40 in an orbital,linear or oscillatory pattern or any combination thereof.

[0036] Platen 50 may have one or two, but preferably a plurality of,channels 110 for the transportation of an electrolytic planarizingsolution to a surface 40 a of polishing pad 40 from a manifold apparatus(not shown) or any suitable fluid distribution system. Alternatively, itwill be appreciated that the electrolytic planarizing solution may bedeposited directly on or through surface 40 a of polishing pad by aconduit or any suitable application mechanism.

[0037] Electrolytic planarizing solutions containing electrolytessuitable for use in the present invention are well known in the art. Theelectrolytic planarizing solution may include concentrated mineral acidssuch as phosphoric acid, sulfuric acid, chromic acid, perchloric acid,or mixtures thereof. Metaphosphoric acid, pyrophosphoric acid,polyphosphoric acid, and ammonium phosphate may also be used. Salts maybe used in addition to or in place of acids in the solution, such asalkali and alkali earth metal salts of halides, carboxylates, andnitrates. Transition metal salts such as copper sulfate, copper nitrateand the like may also be included. In addition to these compounds, theelectrolytic planarizing solution may also include a conventional CMPslurry to facilitate chemical mechanical planarization.

[0038] The electrolytic planarizing solution may also include a filmforming agent which includes any compound or mixture of compounds thatfacilitates the formation of a passivation film of metal oxides anddissolution-inhibiting layers on the metallized surface of wafer 60. Thepassivation film reduces, and preferably eliminates, wet etching of thelow topography areas of the metallized surface 80 of wafer 60 until thelow topography areas come in contact with polishing pad 40. When theselow topography areas come in contact with polishing pad 40 andelectrical conductors 70, described below, the passivation film isremoved and electrochemical etching may proceed. Thus, the passivationfilm enhances uniform planarization of wafer 60. Suitable film formingagents may be formed of nitrogen-containing cyclic compounds such asproline, adedine, mercaptonitriles, imidazole, triazole, benzotriazole,benzimidazole and benzothiazole and their derivatives with hydroxy,amino, imino, carboxy, mercapto, nitro and alkyl substituted groups, aswell as urea, thiourea and others. Other suitable film forming agentsmay include benzofuroxan, benzothiadiazole, phenylenediamine, catechol,amionpheno, mercaptobenzthiazole, mercaptobenztriazole,mercaptobenoxazole, melamine and thiadiazole.

[0039] The electrolytic planarizing solution may also include oxidizersto facilitate planarization. Oxidizers may be used in the electrolyticplanarizing solution to tailor the oxidation-reduction potential of thesolution for a desired application. Oxidizers may also be used tocontrol the electric current density and to reduce the formation ofbubbles which may cause non-uniform electropolishing. Suitable oxidizersmay include hydrogen peroxide, ferricyanide, bisulfate, monopersulfate,periodate, perchlorate, and other “per” compounds and anions, nitrate,hypochorite, hydroxylamine (HDA) and hydroxylamine derivatives,including chloride, sulfate, nitrate and other salt derivatives.

[0040] Complexing agents also may be used in the electrolyticplanarization solution. During the planarization of a metal layer,organic and metal ions and metal oxide may rapidly form on the etchedmetal layer, repassivating the metal layer. As described in more detailbelow, polishing pad 40 may be urged against wafer 60 with a relativelylow force, preferably no more than 1 psi. This low force may not besufficient to remove the repassivation layer so that electrochemicalplanarization may proceed. Complexing agents may be used to achieveacceptable planarization rates by inhibiting the formation ofundesirable repassivation layers. Complexing agents also may preventviscous gels formed of metal ion-saturated electrolytic planarizingsolution from collecting on the wafer and the electrical conductors.

[0041] Suitable complexing agents include amines or compounds possessingamine-like characteristics. In one embodiment of the invention in whichthe metallized layer is formed of copper, the complexing agent mayinclude glycine. Glycine forms a chelate complex with copper ions thatinhibits the formation of copper oxide repassivation films. Othersuitable complexing agents may include ethylenediaminetetracetic acidand salts thereof, ethylene diamine, 1,8-diazabicyclo [5.4.0]undec-7-ene, 1,4-diazabicyclo [2.2.2] octane, ethylene glycol, crownethers, catechol and gallol. Other useful complexing agents may beformed of acids, such as citric, lactic, malonic, tartaric, succinic,malic, acetic and oxalic acid, as well as amino acids, sulfamic andamino sulfuric acids, phosphoric acids, phosphonic acids, 2-quinolinecarboxylic acid, and their salts. Flouride and fluoride-containingcompounds that are capable of producing active fluoride, such asflouboric acid, fluotitanic acid, hydrofluoric acid, fluosilicic acidand the like, and their salts, may also be used.

[0042] Additives which modify and control the viscosity of theelectrolytic planarizing solution may also be included. Such additivesmay optimize viscosity to reduce turbulent flow of the electrolyticplanarizing solution which may result in non-uniform electrochemicaletching. Such additives may include glycerol, glycerin, alcohols, suchas methanol, ethanol, propanol and the like, and ester and ethersolvents, such as ethylene glycol monobutylether. Polymeric additivessuch as polyacrylic acid, propylene oxide, polyethylene oxide andpolyvinylalcohol may also be used if they are soluble in the highlyionic electrolytic planarizing solution.

[0043] Surfactants may also be a useful component of the electrolyticplanarizing solution. Sufactants may be used to facilitate wetting ofthe metal layer, the passivation film formed by the film forming agent,and the electrical conductors to prevent bubbles from adhering to thosesurfaces.

[0044] Polishing pad 40 may be formed of a polymeric material, apolymetric/inorganic composite “fixed abrasive” material or a ceramicinsulator material. The hardness and density of polishing pad 40 areselected based on the type of material to be planarized. Blownpolyurethane pads, such as the IC and GS series of pads available fromRodel Products Corporation of Scottsdale, Ariz., may be advantageouslyutilized by the ECP apparatus, although it will be appreciated that anysuitable polishing pad may be used. Polishing pad 40 has a thicknesswhich may range from approximately 200 angstroms to approximately 3 mm.However, the current density and, accordingly, the removal rate of themetallized surface 80 of wafer 60, is inversely proportional to thedistance between platen 50, which acts as a cathode when an electricpotential is applied, and the metallized surface 80, which acts as ananode.

[0045] As illustrated in FIGS. 4 and 5, polishing pad 40 may haveapertures 210 through which the electrolytic planarizing solution fromchannels 110 may flow. In addition, polishing pad 40 may have grooves120. Grooves 120 are configured to effect transportation of theelectrolytic planarization solution on polishing pad 40 duringplanarization. Polishing pad 40 may also be porous, further facilitatingtransportation of the electrolytic planarization solution. Apertures 210may also be configured to expose portions of platen 50 which acts as acathode when an electric potential is applied between the metallizedsurface 80 of wafer 60 and platen 50. Because polishing pad 40 is formedof insulative material, apertures 210 act to direct the electric fieldfrom platen 50 (cathode) to the metallized surface 80 (anode) of wafer60. In an alternative embodiment, as illustrated in FIG. 9, polishingpad may have cut-out portions, or “windows” 220, preferably positionedwithin grooves 120, which expose portions of platen 50 to facilitate anelectric potential difference between platen 50 and the metallizedsurface of wafer 80. It will be appreciated, however, that polishing pad40 may have any suitably-shaped openings that are configured to producea uniform electric field at desired areas of the wafer.

[0046] Referring again to FIG. 4, at least one electrical conductor 70is positioned within platen 50. While FIG. 4 shows a plurality ofelectrical conductors 70 positioned within platen 50, it will beappreciated that one, two or any suitable number of electricalconductors 70 may be positioned within platen 50. Electrical conductors70 are connected at a first end to a power source 90 and are insulatedwithin platen 50 by insulation elements 230. Each of the electricalconductors 70 may include at a second end a contact element 100. Atleast a portion of contact element 100 is positioned within polishingpad 40. A top surface 100 a of contact element 100 may be positionedabove or below top surface 40 a of polishing pad 40 but is preferablypositioned flush with the top surface 40 a of polishing pad 40. Contactelement 100 is formed of any suitable material that exhibits lowelectrical resistance and resistance to corrosion and is softer than themetal that comprises the metallized surface 80 of wafer 60. For example,if the metallized surface 80 of wafer 60 is formed of copper, contactelement 100 may be formed of a conductively-enhanced polymer material,ceramic material or inorganic fibers such as, for example, carbonfibers.

[0047] An electric potential difference is effected between platen 50and the metallized surface 80 of wafer 60 via electrical conductors 70.Power source 90 applies a negative charge to platen 50 and applies apositive charge to electrical conductors 70. The positive charge isconducted through electrical conductors 70, through contact elements 100and the electolytic planarizing solution and then to metallized surface80 of wafer 60. Positioning of the electrical conductors within theplaten facilitates creation of a uniform electric potential gradientacross the surface of the wafer reducing the likelihood that edgeeffects and the like may result. The distance between the metallizedsurface 80 of wafer 60 and platen 50 is an important factor in theselectivity of the etching process. The distance may be less than 3 mmbut is preferably less than 1 mm and is more preferably less than 2000angstroms. However, to avoid shorting of the circuit formed from platen50 through the electolytic planarizing solution to metallized surface80, the platen should not contact the metallized surface.

[0048] The apparatus of the present invention may also include atemperature control mechanism. The temperature of the metallized surface80 of wafer 60 during electrochemical planarization may have asignificant effect on the uniformity of the metal removal rate. If thetemperature is too high in a given area, electric current mayconcentrate in that area, causing localized hot spots where metal iondissolution is occurring at a faster rate than surroundinglower-temperature areas. To counteract the generation of localized hotspots, in one embodiment of the present invention the electrolyticplanarizing solution may be cooled before being delivered to the surface40 a of polishing pad 40. In this embodiment, the electrolyticplanarizing solution may be subjected to a chiller (not shown) beforebeing delivered to the platen 50.

[0049] In an alternative embodiment of the invention, the temperature ofthe electrochemical planarization process may be controlled by providinga heat exchange fluid to the backside of wafer 60. Apparatus forexposing a heat exchange fluid to the backside of a wafer are well knownin the art. For an example of an apparatus configured to regulate thepolishing rate of a wafer by backside heat exchange, see U.S. Pat. No.5,605,488, issued to Ohashi et al. on Feb. 25, 1997, which patent isherein incorporated by reference.

[0050] The temperature of the electrochemical planarization process mayalso be regulated by providing a heat conductivity platen configured tobe temperature controlled by a heat exchange fluid circulatingtherethrough. Although there are a number of methods to fabricate such aplaten, only one of those methods is illustrated herein. Referring toFIG. 10, in accordance with one embodiment of the invention, platen 400is fabricated from a material having a high thermal conductioncoefficient to facilitate control of the processing temperature. Platen400 may be constructed in three pieces that are connected together bybelts, rivets or, preferably, by brazing to form a unitary platen.Platen 400, in this embodiment, is formed from a substantially circularcover plate 410 that has a substantially planar upper surface 420 towhich a polishing pad can be attached, for example, with an adhesive. Inthis embodiment, platen 400 further includes a channel section 430 thatincludes channel grooves 440. Preferably, channel grooves 440 areconfigured in a serpentine pattern. A heat exchange fluid flows frominlets 450 near the center or axis of platen 400 to a location near theperiphery 460 of the platen and then, in a serpentine pattern to exits480 again located near the center or axis of platen 400. Platen 400 iscompleted by a bottom section 490 that includes on its bottom surface(not show) a configuration for the attachment of the platen to a platenshaft.

[0051] In an alternative method (not illustrated) for fabricating platen400, the channel groove could be formed in the underside of the coverplate. The channel groove could then be sealed by attaching a circulardisk having a planar top surface to the underside of the cover plate.The bottom section could then be attached to the circular disk, or,alternatively, the function of the circular disk and the bottom sectioncould be combined. In either this method or the illustrated method, achannel groove through which a heat exchange fluid can be circulated isformed beneath the substantially planar surface of the platen assembly.

[0052] Cover plate 410, channel section 430 and bottom section 490 eachhave a first set of channels 500, similar to channels 110 as referencedin FIG. 4, through which an electrolytic planarizing solution may flow.Channels 500 in cover plate 410 are colinear with channels 500 inchannel section 430, which in turn are colinear with channels 500 inbottom section 490. A manifold apparatus (not shown) may be connected tobottom section 490 to deliver the electrolytic planarizing solutionthrough channels 500 of the bottom section, channel section and coverplate to the polishing pad.

[0053] In addition to channels 500, cover plate 410, channel section 430and bottom section 490 have bores 510. Bores 510 in cover plate 410 arecolinear with bores 510 in channel section 430, which in turn arecolinear with bores 510 in bottom section 490. When the cover plate,channel section and bottom section are connected together to formunitary platen 400, electrical conductors 70 may be seated within bores510.

[0054] A method for electrochemical planarization using one embodimentof the invention will now be described. Referring again to FIG. 4, wafercarrier 130 urges wafer 60 against polishing pad 40 such that wafer 60engages polishing pad 40 at a desired pressure. Preferably, the wafercarrier applies a uniform and constant pressure of approximately 1 psior less, although it may be appreciated that any suitable pressure whichpromotes planarization without interfering with the concurrentelectrochemical etching process may be used. Alternatively, to furthercontrol the rate of metal removal, the wafer carrier may press the waferagainst the polishing pad for a predetermined amount of time,subsequently withdraw the wafer from the polishing pad for apredetermined amount of time, and then repeat the pressing/withdrawingpattern a desired number of times. For example, the wafer carrier may“bump” the wafer against the polishing pad for a predetermined number oftimes to control the removal rate of the metallized surface.

[0055] During the planarization process, an electrolytic planarizingsolution is delivered to the surface of polishing pad 40 throughchannels 110 and aperatures 210. An electric potential is also appliedto create a circuit between platen 50, the electrolytic planarizingsolution and metallized surface 80 of wafer 60. The power source 90 mayapply a constant current or voltage to the apparatus or, alternatively,the current or voltage could be modulated to apply different currents orvoltages at predetermined times in the process or to modulate between apredetermined current or voltage and no current or no voltage. Wafercarrier 130 and wafer 60 may rotate about an axis 140 while platen 50and polishing pad 40 move in a rotational, orbital or linear pattern. Inaddition, wafer carrier 130 and wafer 60 may oscillate relative topolishing pad 40. Adjusting the various conditions of theelectrochemical planarization process, such as the electric potential,distance between the electric conductors and the metallized surface,conductivity of the electrolytic planarizing solution, temperature,hydrodynamic conditions, and mechanical integrity of the passivationfilm, permits suitable control over the uniformity and rate of removalof metal from the metallized surface.

[0056]FIG. 6 illustrates semiconductor wafer 60 undergoing planarizationusing the apparatus and method of the present invention. Wafer 60 mayhave layers 170 of low dielectric constant material or oxide materialunderlying metallized surface 80. During planarization, electrochemicaletching takes place, during which metal ions from metallized surface 80are liberated from wafer 60. As the high topography areas 150 of themetallized surface 80 of wafer 60 come in contact with the contactelements 100, an electric potential is effected between platen 50, whichacts as a cathode, and metallized surface 80 of wafer 60, which acts asan anode. An electrolytic planarizing solution is delivered to themetallized surface 80 of wafer 60 through channels 110 and apertures 210and is distributed through grooves 120. The film forming agent of theelectrolytic planarizing solution forms a soft surface film 160 over themetallized surface 80 of wafer 60. The film forming agent acts toprotect the low topography areas 180 of the metallized surface 80 fromelectrochemical etching until these areas come in contact with contactelements 100, thereby facilitating uniform planarization of wafer 60.

[0057] The electric current between the cathode and the anode isinversely proportional to the distance from platen 50 and metallizedsurface 80 and, accordingly, the thickness of polishing pad 40. Adistance 190 a from platen 50 to high topography areas 150 is less thana distance 190 b from platen 50 to low topography areas 180;consequently, the rate of removal of metal ions from high topographyareas 150 is greater than the rate of removal of metal ions from lowtopography areas 180. In addition, as planarization proceeds, polishingpad 40 performs a “brushing” action on the wafer, thereby effectingmechanical planarization of wafer 60.

[0058] As illustrated in FIG. 7, after planarization is completed, anyremaining metal from the metallized surface and any remaining barrierlayer 200 may be removed by standard etching processes, such as wetetch, vapor etch, spray etch, plasma or even CMP, since the surface ofthe wafer had just previously been substantially planarized with thepresent invention. Alternatively, a second electrochemical planarizingsolution may be supplied through channels 110 and apertures 210 to thepolishing pad. The second electrochemical planarizing solution may havea different composition, for example, different electrolytes, from thefirst electrochemical planarizing solution so that the second solutionis more suitable for electrochemical etching of another metal layer,such as barrier layer 200.

[0059] In one embodiment of the invention, for example, two or moresources of electrolytic planarizing solution may be connected to thepolishing apparatus. Referring to FIG. 11, channels 110 may be connectedto a manifold apparatus 600. Manifold apparatus 600 may be connected toa feed tube 610 which is in fluid communication with a firstelectrolytic planarizing solution source 620 and a second electrolyticplanarizing solution source 630 through a first source tube 640 and asecond source tube 650, respectively. At the commencement ofplanarization, a first switch 660 may be opened to allow a firstelectrolytic planarizing solution from first electrolytic planarizingsolution source 620 to flow through first source tube 640, feed tube610, manifold apparatus 600, and channels 110 to the surface ofpolishing pad 40. During the flow of the first electrolytic planarizingsolution, a second switch 670 is closed to prevent the flow of a secondelectrolytic planarizing solution from second electrolytic planarizingsolution source 630. The first electrolytic planarizing solution mayinclude compounds suitable for uniformly and effectively etching a firstmetal layer on wafer 60. When the first metal layer has beensubstantially removed from wafer 60, switch 660 may be closed and switch670 may be opened to permit the second electrolytic planarizing solutionfrom electrolytic planarizing solution source 630 to flow through secondsource tube 650, feed tube 610, manifold apparatus 600 and channels 110to the surface of polishing pad 40. The second electrolytic planarizingsolution may include compounds suitable for uniformly and effectivelyetching a second metal layer, for example, a barrier metal layer, onwafer 60. While the illustrated embodiment of the present inventionutilizes two electrolytic planarizing solutions, it will be appreciatedthat any suitable number of electrolytic planarizing solutions may beused to electrochemically etch the various metal layers of metallizedsurface 80 of wafer 60.

[0060] The ECP apparatus of the present invention facilitates concurrentelectrochemical etching and chemical mechanical planarization, such thatthe metal layer is removed first from high topography areas of thewafer, producing more uniformly planarized wafers. The electrochemicaletching aspect of the invention enables high removal rates at lowpressures, which reduces dishing and oxide erosion.

[0061]FIG. 8 illustrates another alternative embodiment of a platen 300of the present invention in which a platen 300 may have “zones” ofelectrical conductors to which different currents are supplied. Becausethe center of a wafer carrier rotates at a lower velocity at its centerthan at its periphery, a wafer carried by the wafer carrier may exhibita faster removal rate of the metallized surface at the periphery of thewafer compared to the center of the wafer. To counteract thisnon-uniform removal across the surface of the wafer, use of “zones” ofelectrical conductors supplied with different currents may be used. Forexample, in a first zone 310 one or more electrical conductors 320 maybe connected to a first power supply which supplies a first current. Ina second zone 330 one or more electrical conductors 340 may be connectedto a second power supply which supplies a second current which isdifferent from the first current. The first zone and the second zone maybe separated by a first insulator 350. In addition, platen 300 may havea third zone 360 which has one or more electrical conductors 370connected to a third power supply which supplies a third current, whichmay be equivalent to the first current or may be different from both thefirst and the second currents. The third zone may be separated from thesecond zone by a second insulator 380. While FIG. 8 shows three zones ofelectrical conductors to which two or more currents are supplied, itwill be appreciated that platen 300 may have four or more zones withelectrical conductors to which are supplied any suitable currents.Platen 300 may further have channels 390 through which an electrolyticplanarizing solution is supplied. Using this embodiment, the electricpotential supplied to different areas of a wafer may be used to reduceedge effects which result when the peripheral edges of the wafer areplanarized at a different rate than the center of the wafer.

[0062] In another embodiment (not illustrated), the present inventionmay be configured for endpoint detection. Referring again to FIG. 6, asthe metallized surface 80 of wafer 60 is removed during theplanarization process, the resistance of the metallized surface 80increases, thereby increasing the voltage through wafer 60. This changein the electric potential between the metallized surface and the platenmay be monitored to determine the desired endpoint of the planarizationprocess. Accordingly, the present invention provides the advantage ofin-situ endpoint detection without requiring an additional dedicatedendpoint detection system.

[0063] In the foregoing specification, the invention has been describedwith reference to specific embodiments. However, it may be appreciatedthat various modifications and changes can be made without departingfrom the scope of the present invention as set forth in the claimsbelow. Accordingly, the specification and figures are to be regarded inan illustrative rather than a restrictive sense, and all suchmodifications are intended to be included within the scope of thepresent invention.

[0064] Benefits, other advantages, and solutions to problems have beendescribed above with regard to specific embodiments. However, thebenefits, advantages, solutions to problems, and any element(s) that maycause any benefit, advantage, or solution to occur or become morepronounced are not to be constructed as critical, required, or essentialfeatures or elements of any or all of the claims. As used herein, theterms “comprises,” “comprising” or any other variation thereof, areintended to cover a non-exclusive inclusion, such that a process,method, article, or apparatus that comprises a list of elements does notinclude only those elements but may include other elements not expresslylisted or inherent to such process, method, article or apparatus.

We claim:
 1. An electrochemical planarization apparatus for planarizing a metallized surface on a workpiece, said apparatus comprising: a) a polishing pad; b) a platen comprising conductive material and disposed proximate to said polishing pad, wherein said platen is configured to have a negative charge during at least a potion of a planarization process; c) at least one electrical conductor positioned within said platen and having a first end connected to a power source; and d) a workpiece carrier configured to carry a workpiece and press said workpiece against said polishing pad; wherein said power source applies a positive charge to the workpiece via said at least one electrical conductor so that an electric potential difference between said metallized surface of said workpiece and said platen is created to remove at least a portion of said metallized surface from said workpiece.
 2. The apparatus of claim 1, further comprising a contact element which is formed of low electrical resistance material and is connected to a second end of said at least one electrical conductor and wherein at least a portion of said contact element is positioned within said polishing pad.
 3. The apparatus of claim 1, wherein said polishing pad is made of insulating material.
 4. The apparatus of claim 1, wherein said polishing pad is porous.
 5. The apparatus of claim 1, further comprising a solution application mechanism configured to supply a first electrolytic planarizing solution to a polishing surface of said polishing pad.
 6. The apparatus of claim 5, wherein said solution application mechanism comprises at least one channel formed in said platen through which said electrolytic planarizing solution may flow.
 7. The apparatus of claim 6, wherein said polishing pad has at least one aperture through which said electrolytic planarizing solution from said at least one channel may flow.
 8. The apparatus of claim 7, wherein said at least one aperture is configured to expose a portion of said platen to facilitate creation of said electric potential difference between said platen and said metallized surface.
 9. The apparatus of claim 5, wherein said polishing pad has grooves configured to facilitate distribution of said electrolytic planarizing solution.
 10. The apparatus of claim 1, wherein said polishing pad comprises windows configured to expose portions of said platen to facilitate creation of said electric potential difference between said platen and said metallized surface.
 11. The apparatus of claim 1, wherein said workpiece carrier is configured to cause relative motion between said workpiece and said polishing pad.
 12. The apparatus of claim 11, wherein said relative motion is selected from the group consisting of: linear motion, orbital motion, circular motion, a combination of linear and orbital motion, a combination of linear and circular motion, a combination of orbital and circular motion, and a combination of linear, orbital and circular motion.
 13. The apparatus of claim 1, wherein said platen is configured to move in at least one of an orbital, circular and linear pattern.
 14. The apparatus of claim 1, wherein at least a portion of said platen comprises at least one of aluminum, titanium, gold, copper, tantalum and platinum.
 15. The apparatus of claim 5, wherein said electrolytic planarizing solution comprises at least one of electrolytes, oxidizers, complexing agents, surfactants and viscosity-controlling additives.
 16. The apparatus of claim 1, wherein said metallized surface is of a material selected from the group consisting of: Cu, Cu/Al, Ni, Ag, Au, Ta, TaN, Ti, TiN, W, CoWP, NiP, and CoP.
 17. The apparatus of claim 2, wherein said contact element is formed of at least one of conductively-enhanced polymer material, ceramic material and inorganic fibers.
 18. The apparatus of claim 1, wherein said workpiece carrier is configured to press said workpiece against said polishing pad at a pressure no greater than approximately 1 psi.
 19. The apparatus of claim 5, wherein said electrolytic planarizing solution comprises at least one of a mineral acid, a salt, an oxidizer, a complexing agent, a viscosity agent, and a surfactant.
 20. The apparatus of claim 5, wherein said electrolytic planarizing solution comprises a film forming agent for facilitating the formation of a passivation layer on the metallized surface of the workpiece.
 21. The apparatus of claim 20, wherein said film forming agent comprises nitrogen-containing cyclic compounds.
 22. The apparatus of claim 20, wherein said film forming agent comprises at least one of imidzole, benzotriazole, benzimidazole, benzothiazole, adenine, proline, quinaldic acid, triazole, benzofuroxan, benzothiadiazole, phenylenediamine, catechol, amionpheno, mercaptobenzthiazole, mercaptobenztriazole, mercaptobenoxazole, melamine and thiadiazole.
 23. The apparatus of claim 1, further comprising at least a first group and a second group of electrical conductors, wherein said power source supplies a first current to said first group and a second current to said second group, said first current being different from said second current.
 24. The apparatus of claim 1, further comprising an endpoint detection apparatus configured to monitor a change in said electric potential difference between the metallized surface and said platen and to detect an endpoint of planarization of the workpiece.
 25. The apparatus of claim 1, wherein said electric potential difference alternates between a first electric potential difference and a second electric potential difference.
 26. The apparatus of claim 25, wherein said first electric potential difference is zero.
 27. The apparatus of claim 1, wherein said electrical potential difference is constant.
 28. The apparatus of claim 1, further comprising a temperature control mechanism for counteracting the generation of heat at the metallized surface during planarization.
 29. The apparatus of claim 28, further comprising a solution application mechanism configured to supply an electrolytic planarizing solution to a polishing surface of said polishing pad and wherein said temperature control mechanism comprises a cooler for cooling said electrolytic planarizing solution before said solution is applied to said polishing pad.
 30. The apparatus of claim 28, wherein said workpiece carrier comprises a heat exchange fluid for regulating the temperature of said workpiece.
 31. The apparatus of claim 1, wherein said platen comprises heat conductivity material and wherein said platen is configured to be temperature controlled by a heat exchange fluid circulating therethrough.
 32. The apparatus of claim 1, wherein a distance between said platen and the metallized surface of the workpiece is not greater than approximately 3 mm.
 33. The apparatus of claim 32, wherein said distance is no greater than approximately 1 mm.
 34. The apparatus of claim 33, wherein said distance is no greater than approximately 2000 angstroms.
 35. The apparatus of claim 5, wherein said solution application mechanism is configured to supply a second electrolytic planarizing solution to a polishing surface of said polishing pad.
 36. A method of planarizing a metallized surface on a workpiece, the method comprising: a) providing a polishing pad; b) providing a platen formed of a conductive material and disposed proximate to said polishing pad; c) providing at least one electrical conductor disposed within said platen; d) pressing said workpiece against said polishing pad while causing relative motion between said workpiece and said polishing pad; e) supplying a first electrolytic solution to a polishing surface of said polishing pad; and f) applying an electric potential difference between said metallized surface on said workpiece and said platen during said pressing to remove at least a portion of said metallized surface from the workpiece.
 37. The method of claim 36, wherein said electrolytic planarizing solution is supplied to said polishing surface through at least one channel formed in said platen.
 38. The method of claim 36, wherein said relative motion is chosen from the group consisting of: linear motion, orbital motion, circular motion, a combination of linear and orbital motion, a combination of linear and circular motion, a combination of orbital motion and circular motion, and a combination of linear, orbital and circular motion.
 39. The method of claim 36, further comprising moving said platen in at least one of an orbital, circular or linear pattern.
 40. The method of claim 36, wherein applying an electric potential differences comprises applying a constant electric potential difference.
 41. The method of claim 36, wherein applying an electrical potential difference comprises applying an electric potential difference which alternates between a first electric potential difference and a second electric potential difference.
 42. The method of claim 41, wherein said first electric potential difference is zero.
 43. The method of claim 36, wherein said pressing said workpiece against said polishing pad comprises pressing said workpiece against said polishing pad at a pressure no greater than approximately 1 psi.
 44. The method of claim 36, further comprising providing at least a first group of electrical conductors and a second group of electrical conductors, wherein said first group is supplied with a first current and said second group is supplied with a second current.
 45. The method of claim 36, further comprising supplying a second electrolytic planarizing solution to a polishing surface of said polishing pad.
 46. The method of claim 36, further comprising cooling said first electrolytic planarizing solution before supplying said solution to said polishing pad.
 47. The method of claim 36, wherein providing a platen comprises providing a platen of heat conductivity material through which a heat exchange fluid circulates.
 48. The method of claim 36, further comprising circulating a heat exchange fluid proximate a surface of said workpiece to counteract the generation of heat at the metallized surface of the workpiece.
 49. The method of claim 36, further comprising, during said pressing, maintaining a distance between said platen and the metallized surface of no greater than 3 mm.
 50. The method of claim 36, further comprising, during said pressing, maintaining a distance between said platen and the metallized surface of no greater than 1 mm.
 51. The method of claim 36, further comprising, during said pressing, maintaining a distance between said platen and the metallized surface of no greater than 2000 angstroms.
 52. The method of claim 36, further comprising monitoring a change in said electric potential difference to detect an endpoint of planarization of the workpiece.
 53. The method of claim 36, wherein said supplying a first electrolytic solution comprises supplying an electrolytic solution having at least one of a mineral acid, a salt, an oxidizer, a complexing agent, a viscosity agent, and a surfactant.
 54. The method of claim 36, wherein said supplying a first electrolytic solution comprises supplying an electrolytic solution having a film-forming agent for facilitating the formation of a passivation layer on the metallized surface of the workpiece.
 55. The method of claim 36, wherein said supplying a first electrolytic solution comprises supplying an electrolytic solution having a film-forming agent formed of nitrogen-containing cyclic compounds.
 56. The method of claim 36, wherein said supplying a first electrolytic solution comprises supplying an electrolytic solution having a film-forming agent comprised of at least one of imidzole, benzotriazole, benzimidazole, benzothiazole, adenine, proline, quinaldic acid, triazole, benzofuroxan, benzothiadiazole, phenylenediamine, catechol, amionpheno, mercaptobenzthiazole, mercaptobenztriazole, mercaptobenoxazole, melamine and thiadiazole.
 57. An apparatus for removing metal from a metallized surface of a workpiece, comprising: a) a polishing pad; b) an electrically conductive surface disposed proximate to said polishing pad; c) at least one conducting element disposed proximate the metallized surface of the workpiece and remote from an edge of said metallized surface; d) a workpiece carrier configured to press the workpiece against said polishing pad; and e) a power source configured to apply an electric potential between the metallized surface of the workpiece and the electrically conductive surface.
 58. The apparatus of claim 57, further comprising at least one passage disposed in said polishing pad so that the metallized surface of the workpiece and said electrically conductive surface are in fluid communication through said passage when the workpiece is pressed against said polishing pad.
 59. The apparatus of claim 58, wherein said electrically conductive surface comprises the surface of a polishing platen.
 60. The apparatus of claim 59 further comprising a conduit disposed in said polishing platen, wherein said conduit is in fluid communication with said passage.
 61. The apparatus of claim 57, wherein said polishing pad comprises a plurality of first parallel grooves.
 62. The apparatus of claim 61, wherein said polishing pad comprises a plurality of second parallel grooves positioned in intersecting relation with said first parallel grooves.
 63. The apparatus of claim 62, further comprising at least one fluid passage disposed in said polishing pad, wherein said at least one fluid passage is in fluid communication with at least one of said first and second parallel grooves.
 64. The apparatus of claim 63, wherein said electrically conductive surface comprises a polishing platen having at least one conduit positioned therethrough, and wherein said at least one conduit is in fluid communication with said at least one fluid passage.
 65. The apparatus of claim 57, further comprising a contact element formed of low electrical resistance material connected to said conducting element, wherein said contact element is in electrical communication with said conducting element and the metallized surface.
 66. The apparatus of claim 57, wherein said workpiece carrier is configured to cause relative motion between said workpiece and said polishing paid. 